Why we have leap year

Wednesday

Feb 27, 2008 at 12:01 AMFeb 27, 2008 at 4:10 PM

Understanding the reasoning behind a leap year can be perplexing with the way calendars have evolved through the centuries.

Staff reports

Understanding the reasoning behind a leap year can be perplexing with the way calendars have evolved through the centuries.
The year 2008 is a leap year, which means that it has 366 days instead of the usual 365.
Years with 365 days in it are refereed to as common years. An extra day is added in a leap year called an intercalary day or a leap day. This occurs on the last day in February.
The leap year was introduced to align the Earth’s rotation around the sun with the seasons. It takes approximately 365.2422 days – or to be precise, 365 days, 5 hours, 48 minutes and 46 seconds – for the Earth to travel around the sun in one year.
A solar year is the time it takes the Earth to complete its orbit around the Sun. Since the Earth does not rotate around the sun in exactly 365 days, a leap year was inserted to align the seasons with the months.
About every four years, the Gregorian calendar, the calendar that is currently in use in the United States, is given one extra day to account for the additional time the Earth requires to travel around the sun.
It may not seem like much of a difference, but after a few years those extra quarter days in the solar year begin to add up. Using a calendar with 365 days every year would result in a loss of 0.2422 days or almost six hours per year.
After four years, the four extra quarter days would make the calendar fall behind the solar year by about a day. Over the course of a century, the difference between the solar year and the calendar year would be about 25 days.
The Gregorian calendar has a number of weaknesses despite it’s widespread use. It cannot be divided into equal halves or quarters, the number of days per month is haphazard and months or even years may begin on any day of the week. The Gregorian calendar is also off by 27 seconds every year, which produces one extra day every 3,236 years.
Prior to adoption of the Gregorian calendar ordered by Pope Gregory XIII in 1582, the Julian calendar was widely used. The Julian calendar was introduced by Julius Caesar in 46 BC.
In the Gregorian calendar, the calendar used by most modern countries, certain criteria must be met to determine which years will be leap years. Every year that is divisible by four is a leap year.
Of those years, if it can be divided by 100, it is not a leap year unless the year is divisible by 400.
In ancient times, it was customary to have lunar or moon calendars, with 12 or 13 months every year. To align the calendar with the seasons, the 13th month was inserted as a “leap month” every two or three years. Many countries, especially those in Asia, still use lunar calendars.
The cycles of the sun and moon do not synchronize well. A lunar year consists of 12 lunar cycles that are each 29 and a half days long and is 354 days, 8 hours long. After three years, a lunar calendar would deviate from the solar calendar by 33 days.
The Gregorian calendar has a 400-year cycle until it repeats the same weekdays for every year, Feb. 29, 2008, is a Friday and Feb. 29, 2408, is a Friday. The Gregorian calendar has 97 leap years during those 400 years. The longest time between two leap years is eight years. The last time that occurred was between 1896 and 1904. The next time will be between 2096 and 2104.
The information sited in this story was collected from www.infoplease.com and www.timeanddate.com.
Lake Sun Leader

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